Showing papers by "University of Bremen published in 2000"

Transnationalization in international migration: implications for the study of citizenship and culture

Abstract: Terms such as transnational social spaces, transnational social fields or transnationalism usually refer to sustained ties of persons, networks and organizations across the borders across multiple nation-states, ranging from little to highly institutionalized forms. However, there are two large conceptual gaps in the study of transnational social spaces arising out of international migration and refugee flows. First, terms such as transnational social spaces and transnational communities are often used synonymously, as if 'transnational community' were the only form or type of transnational social space. This analysis outlines the primary mechanisms operative in transnationalization: reciprocity in small groups, exchange in circuits and solidarity in communities. These mechanisms correspond to distinct types of transnational social spaces - transnational kinship groups, transnational circuits and transnational communities. Second, the implications of transnationalization for citizenship and culture have n...

Rapid changes in the hydrologic cycle of the tropical Atlantic during the last glacial.

Abstract: Sedimentary time series of color reflectance and major element chemistry from the anoxic Cariaco Basin off the coast of northern Venezuela record large and abrupt shifts in the hydrologic cycle of the tropical Atlantic during the past 90,000 years. Marine productivity maxima and increased precipitation and riverine discharge from northern South America are closely linked to interstadial (warm) climate events of marine isotope stage 3, as recorded in Greenland ice cores. Increased precipitation at this latitude during interstadials suggests the potential for greater moisture export from the Atlantic to Pacific, which could have affected the salinity balance of the Atlantic and increased thermohaline heat transport to high northern latitudes. This supports the notion that tropical feedbacks played an important role in modulating global climate during the last glacial period.

Modularity in development and evolution.

Abstract: This work offers a sustained exploration of modules from developmental and evolutionary perspectives. Contributors discuss what modularity is, how it can be identified and modeled, how it originated and evolved, and why it matters.

Democratic Governance Beyond the Nation-State:: The EU and Other International Institutions

Abstract: International institutions not only increase system effectiveness or output legitimacy, but are also a normatively plausible response to the problems for democracy that are caused by globalization. In this way, international institutions also increase input legitimacy. It is therefore a false approach to pin down the problem of democracy beyond the nation-state as a choice between `effective problem-solving through international institutions' and `democratic political processes'. At the same time, it is indisputable that the actual functioning of these international institutions does not meet democratic standards. By correctly pointing to the deficits of current international institutions, sceptics too quickly conclude that most deficits in the working of international institutions cannot be remedied. The sceptical argument is founded on two more or less explicit background hypotheses that can be empirically challenged. The first background hypothesis states that a demos cannot exist at the transnational ...

Predictability of the toxicity of multiple chemical mixtures to Vibrio fischeri: Mixtures composed of similarly acting chemicals

Abstract: The prediction of combined effects based on the effects of the individual components of mixtures by using the pharmacological concepts of concentration addition and independent action might be a promising tool for the risk assessment of pollutant mixtures. To analyze and compare the predictive capabilities of the reference concepts for similarly acting chemicals, the overall toxicity of a multiple mixture was determined in a bioluminescence inhibition assay with Vibrio fischeri. The mixture was composed of 16 similarly and specifically acting chemicals, anticipated to have a common mode of action via weak acid respiratory uncoupling of oxidative phosphorylation. Results show that the observed mixture toxicity is rather well predicted by both concepts. Concentration addition shows an excellent predictive power; the median effective concentration (EC50) of the mixture is predicted with an error of about 10%. Independent action, in contrast, underestimates the EC50 of the mixture by a factor of a little more than three. With respect to risk assessment procedures, it may be concluded that concentration addition gives a valid estimation of the overall toxicity for multiple mixtures with similar and specific mechanisms of action of the mixture components in this type of biotest.

Cigarette smoking and bladder cancer in men: a pooled analysis of 11 case-control studies.

Abstract: The primary risk factor for bladder cancer is cigarette smoking. Using a combined analysis of 11 case-control studies, we have accurately measured the relationship between cigarette smoking and bladder cancer in men. Available smoking information on 2,600 male bladder cancer cases and 5,524 male controls included duration of smoking habit, number of cigarettes smoked per day and time since cessation of smoking habit for ex-smokers. There was a linear increasing risk of bladder cancer with increasing duration of smoking, ranging from an odds ratio (OR) of 1.96 after 20 years of smoking (95% confidence interval [CI] 1.48–2.61) to 5.57 after 60 years (CI 4.18–7.44). A dose relationship was observed between number of cigarettes smoked per day and bladder cancer up to a threshold limit of 15–20 cigarettes per day, OR = 4.50 (CI 3.81–5.33), after which no increased risk was observed. An immediate decrease in risk of bladder cancer was observed for those who gave up smoking. This decrease was over 30% after 1–4 years, OR = 0.65 (0.53–0.79), and was over 60% after 25 years of cessation, OR = 0.37 (0.30–0.45). However, even after 25 years, the decrease in risk did not reach the level of the never-smokers, OR = 0.20. (0.17–0.24). The proportion of bladder cancer cases attributable to ever-smoking was 0.66 (0.61–0.70) for all men and 0.73 (0.66–0.79) for men younger than 60. These estimates are higher than previously calculated. Int. J. Cancer 86:289–294, 2000. © 2000 Wiley-Liss, Inc.

Predictability of the toxicity of a multiple mixture of dissimilarly acting chemicals to Vibrio fischeri

Abstract: A promising tool for the risk assessment of chemical mixtures is the prediction of their toxicities from the effects of the individual components. For that purpose, concentration addition is uniformly regarded as valid for mixtures of similarly acting chemicals. Whether this concept or the competing notion of independent action is more appropriate for mixtures of dissimilarly acting chemicals is still in dispute. Therefore, the presented study analyzed and compared the predictive capabilities of both concepts for a multiple mixture designed of strictly dissimilarly acting compounds. Experimental investigations were conducted using a long-term bioluminescence inhibition assay with Vibrio fischeri. Results show an excellent predictive power of independent action, while concentration addition overestimates the mixture toxicity. Thus, the precise prediction of mixture toxicities depends on a valid assessment of the similarity/dissimilarity of the mixture components. However, concentration addition underestimates the EC50 of the mixture only by a factor of less than three. As the similarity of components is often unknown for mixtures found in the environment, it is concluded that concentration addition may give a realistic worst case estimation of mixture toxicities for risk assessment procedures.

Biomass and abundance

Abstract: Publisher Summary The determination of the total plankton biomass or biovolume is rapid compared with the enumeration and identification techniques. Many samples can be processed in parallel. These measurements are suitable for mixed samples as well as for samples of selected individual species. There is a wide variety of biovolume and biomass measurements. The effort involved in sample treatment increases within the conventional methods and is generally large in biochemical procedures. The methodological bias decreases stepwise: when the amount of excess and interstitial water is reduced by measuring displacement volume or wet mass instead of settled volume, when body fluids are totally removed during dry mass determination, and when the inorganic substances are subtracted. Volumetric methods are the only choice if the samples are to be used for species identification as well. Volumetric methods are also recommended as a quick-look procedure; that is, on board a ship, and in cases where no microbalance or other sophisticated equipment is available. There are two principles related to the volumetric methods: the direct volume estimation of settled plankton and the measurement of the amount of water displaced by the plankton. The first method is more gentle but less precise.

Transport of terrestrial organic carbon to the oceans by rivers: re-estimating flux- and burial rates

Abstract: This study re-estimates one important component in the global carbon cycle: the modern global fluviatile organic carbon discharge- and burial rates. According to these results, approximately 430×1012 g of terrestrial organic carbon are transported to the ocean in modern times. This amount is higher than the latest estimates but takes into account new data from Oceania not previously considered in global flux studies. However, only the minor amount of 10% or approximately 43×1012 gC year–1 is most likely buried in marine sediments. This amount is similar to the burial of marine organic carbon in the coastal ocean (55×1012 gC year–1). Adding both estimates gives approximately 100×1012 gC year–1, which is the value calculated by Berner (1982) for "terrestrial" deltaic-shelf sediments. However, the results in this study suggest that on a global scale the organic carbon content in coastal ocean sediments is not solely of terrestrial origin but a mixture of nearly equal amounts of marine and terrestrial organic carbon. The major part of the terrestrial organic carbon that enters the ocean by rivers (approximately 400×1012 gC year–1) seems to be either (a) remineralised in the ocean, whereas the mechanism by which the terrestrial organic carbon is oxidised in the ocean are unknown; or (b) is dispersed throughout the oceans and accumulates in pelagic sediments.

Upwelling intensification as part of the Pliocene-Pleistocene climate transition.

Abstract: A deep-sea sediment core underlying the Benguela upwelling system off southwest Africa provides a continuous time series of sea surface temperature (SST) for the past 4.5 million years. Our results indicate that temperatures in the region have declined by about 10°C since 3.2 million years ago. Records of paleoproductivity suggest that this cooling was associated with an increase in wind-driven upwelling tied to a shift from relatively stable global warmth during the mid-Pliocene to the high-amplitude glacial-interglacial cycles of the late Quaternary. These observations imply that Atlantic Ocean surface water circulation was radically different during the mid-Pliocene.

Principles of Systems

Abstract: The feedback mechanism involved in all principles for artificial learning refers back to the notion of the control-circuit. This very common concept serves as a basis for the analysis and the design of feedback-control systems.

New chronology for the late Paleocene thermal maximum and its environmental implications

Abstract: The late Paleocene thermal maximum (LPTM) is associated with a brief, but intense, interval of global warming and a massive perturbation of the global carbon cycle. We have developed a new orbital chronology for Ocean Drilling Program (ODP) Site 690 (Weddell Sea, Southern Ocean) by using spectral analysis of high-resolution geochemical records. The LPTM interval spans 11 precessional cycles yielding a duration of 210 to 220 k.y. The δ 13 C anomaly associated with the LPTM has a magnitude of about −2.5‰ to −3‰; we show that about −2‰ of the excursion occurs within two steps that each were less than 1000 yr in duration. The remainder developed through a series of steps over ∼52 k.y. The timing of these steps is consistent with a series of nearly catastrophic releases of methane from gas hydrates, punctuated by intervals of relative equilibria between hydrate dissociation and carbon burial. Further, we are able to correlate the records between ODP Sites 690 and 1051 (western North Atlantic) on the scale of 21 k.y. cycles, which demonstrates that the details of the δ 13 C excursion are recognizable between distant sites. Comparison of cycle records at Sites 690 and 1051 suggests that sediment representing the interval ∼30 k.y. just prior to and at the onset of the LPTM are missing in the latter location. This unconformity probably resulted from slope failure accompanying methane hydrate dissociation within 10 k.y. of the start of the LPTM.

Mutations in a new gene in Ellis-van Creveld syndrome and Weyers acrodental dysostosis

Abstract: Ellis-van Creveld syndrome (EvC, MIM 225500) is an autosomal recessive skeletal dysplasia characterized by short limbs, short ribs, postaxial polydactyly and dysplastic nails and teeth. Congenital cardiac defects, most commonly a defect of primary atrial septation producing a common atrium, occur in 60% of affected individuals. The disease was mapped to chromosome 4p16 in nine Amish subpedigrees and single pedigrees from Mexico, Ecuador and Brazil. Weyers acrodental dysostosis (MIM 193530), an autosomal dominant disorder with a similar but milder phenotype, has been mapped in a single pedigree to an area including the EvC critical region. We have identified a new gene (EVC), encoding a 992-amino-acid protein, that is mutated in individuals with EvC. We identified a splice-donor change in an Amish pedigree and six truncating mutations and a single amino acid deletion in seven pedigrees. The heterozygous carriers of these mutations did not manifest features of EvC. We found two heterozygous missense mutations associated with a phenotype, one in a man with Weyers acrodental dysostosis and another in a father and his daughter, who both have the heart defect characteristic of EvC and polydactyly, but not short stature. We suggest that EvC and Weyers acrodental dysostosis are allelic conditions.

Empirically Grounded Construction of Types and Typologies in Qualitative Social Research

Abstract: In der qualitativen Sozialforschung finden sich nur wenige Ansatze, in denen der Prozes der Typenbildung detailliert expliziert und systematisiert wird; auserdem werden sehr unterschiedliche Typenbegriffe (wie z.B. Idealtypen, Realtypen, Prototypen, Extremtypen, Strukturtypen etc.) verwendet. Da der Typusbegriff fur die qualitative Sozialforschung von zentraler Bedeutung ist, ist eine Klarung des Begriffs sowie des Prozesses der Typenbildung jedoch dringend erforderlich. In dem Beitrag wird daher zunachst eine allgemeine Definition des Typusbegriffs vorgelegt, von der ausgehend Regeln fur eine systematische und nachvollziehbare Bildung von Typen und Typologien formuliert werden. URN: urn:nbn:de:0114-fqs0001145

Manufacturing routes for metallic foams

Abstract: The study of metallic foams has become attractive to researchers interested in both scientific and industrial applications. In this paper, various methods for making such foams are presented and discussed. Some techniques start from specially prepared molten metals with adjusted viscosities. Such melts can be foamed by injecting gases or by adding gas-releasing blowing agents which cause the formation of bubbles during their in-situ decomposition. Another method is to prepare supersaturated metal-gas systems under high pressure and initiate bubble formation by pressure and temperature control. Finally, metallic foams can be made by mixing metal powders with a blowing agent, compacting the mix, and then foaming the compact by melting. The various foaming processes, the foam-stabilizing mechanisms, and some known problems with the various methods are addressed in this article. In addition, some possible applications for metallic foams are presented.

Chaperones in cell cycle regulation and mitogenic signal transduction: a review.

Abstract: Chaperones/heat shock proteins (HSPs) of the HSP90 and HSP70 families show elevated levels in proliferating mammalian cells and a cell cycle-dependent expression. They transiently associate with key molecules of the cell cycle control system such as Cdk4, Wee-1, pRb, p53, p27/Kip1 and are involved in the nuclear localization of regulatory proteins. They also associate with viral oncoproteins such as SV40 super T, large T and small t antigen, polyoma large and middle S antigen and EpsteinBarr virus nuclear antigen. This association is based on a J-domain in the viral proteins and may assist their targeting to the pRb/E2F complex. Small HSPs and their state of phosphorylation and oligomerization also seem to be involved in proliferation and differentiation. Chaperones/HSPs thus play important roles within cell cycle processes. Their exact functioning, however, is still a matter of discussion. HSP90 in particular, but also HSP70 and other chaperones associate with proteins of the mitogen-activated signal cascade, particularly with the Src kinase, with tyrosine receptor kinases, with Raf and the MAP-kinase activating kinase (MEK). This apparently serves the folding and translocation of these proteins, but possibly also the formation of large immobilized complexes of signal transducing molecules (scaffolding function).

The δ15N of nitrate in the Southern Ocean: Nitrogen cycling and circulation in the ocean interior

Abstract: We report analyses of the nitrogen isotopic composition of nitrate in the eastern Indian and Pacific sectors of the Southern Ocean. In this paper, we focus on the subsurface data as well as data from the deep waters of other ocean basins. Nitrate δ15N is relatively invariant in much of the abyssal ocean (i.e., below 2.5 km), with a value of 4.8±0.2‰ observed in Lower Circumpolar Deep Water, North Atlantic Deep Water, and central Pacific deep water. The isotopic invariance of deep ocean nitrate stems fundamentally from the completeness of nitrate utilization in most of the global surface ocean, the Southern Ocean surface being an important exception. In the Subantarctic Zone (north of the Polar Frontal Zone) the nitrate δ15N of Upper Circumpolar Deep Water is ∼0.7‰ greater than that of Lower Circumpolar Deep Water. This isotopic enrichment appears to result from denitrification in the low-latitude water masses with which Upper Circumpolar Deep Water communicates. The isotopic enrichment of Upper Circumpolar Deep Water is diminished in the Antarctic, probably because of the remineralization of sinking organic N, which has a low δ15N in the Antarctic. Relative to the other water masses of the Southern Ocean, the Subantarctic thermocline has a very low nitrate δ15N for its nitrate concentration because of exchange with the low-latitude thermocline, where this isotopic signature appears to originate. This signature of the low-latitude thermocline has two probable causes: (1) mixing with low-nitrate surface water and (2) the oxidation of newly fixed N.

Mass media and the concept of interactivity: an exploratory study of online forums and reader email

Abstract: Lack of interaction between the mass media and their audiences has always been a target for media criticism. While the Internet provides a potential for more interactive communication, one wonders ...

Free-carrier and phonon properties of n- and p-type hexagonal GaN films measured by infrared ellipsometry

Abstract: Infrared spectroscopic ellipsometry (IRSE) over the wave-number range from 300 to 1200 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ is used to determine the anisotropic room-temperature optical properties of highly resistive, Si-doped n-type and Mg-doped p-type \ensuremath{\alpha}-GaN. The approximately 1-\ensuremath{\mu}m-thick films were deposited on c-plane sapphire by molecular beam epitaxy without a buffer layer. The free-carrier concentrations are obtained from Hall measurements. The IRSE data are analyzed through model calculations of the infrared optical dielectric functions parallel (\ensuremath{\parallel}) and perpendicular (\ensuremath{\perp}) to the c axis of the \ensuremath{\alpha}-GaN films. We obtain the thin-film phonon frequencies and broadening values and the optical mobility and effective-mass parameters for n- and p-type \ensuremath{\alpha}-GaN. In agreement with Perlin et al. [Appl. Phys. Lett. 68, 1114 (1996)] we determine the effective electron masses as ${m}_{e,\ensuremath{\perp}}{/m}_{0}=0.237\ifmmode\pm\else\textpm\fi{}0.006$ and ${m}_{e,\ensuremath{\parallel}}{/m}_{0}=0.228\ifmmode\pm\else\textpm\fi{}0.008.$ For p-type GaN with hole concentration ${N}_{h}=8\ifmmode\times\else\texttimes\fi{}{10}^{17}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ we find ${m}_{h}{/m}_{0}=1.40\ifmmode\pm\else\textpm\fi{}0.33,$ which agrees with recent theoretical studies of the Rashba-Sheka-Pikus parameters in wurtzite GaN. However, no substantial anisotropy of the effective hole mass is obtained to within 25%. The ellipsometry data also allow for derivation of the model quantities ${\ensuremath{\epsilon}}_{\ensuremath{\infty},j}$ $(j=\ensuremath{\perp},\ensuremath{\parallel}),$ which are almost isotropic but may vary between 4.92 and 5.37 depending on whether the films are undoped or doped. In heavily-Si-doped n-type \ensuremath{\alpha}-GaN we observe a thin carrier-depleted surface layer and additional infrared-active vibrational modes at 574, 746, and 851 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. Raman measurements of the GaN films are also performed, and the results are compared to those obtained from the IRSE investigations.

Persistent variations in average height between countries and between socio-economic groups: an overview of 10 European countries.

Abstract: Primary objectives: This paper aims to provide an overview of variations in average height between 10 European countries, and between socio-economic groups within these countries.Data and methods: Data on self-reported height of men and women aged 20-74 years were obtained from national health, level of living or multipurpose surveys for 1987-1994. Regression analyses were used to estimate height differences between educational groups and to evaluate whether the differences in average height between countries and between educational groups were smaller among younger than among older birth cohorts.Results: Men and women were on average tallest in Norway, Sweden, Denmark and the Netherlands and shortest in France, Italy and Spain (range for men: 170-179 cm; range for women: 160-167 cm). The differences in average height between northern and southern European countries were not smaller among younger than among older birth cohorts. In most countries average height increased linearly with increasing birth-year...

Linear Theory of Elasticity

Abstract: The linear theory of elasticity, thanks to its relative simplicity and wide applicability, constitutes the principal model of continuum mechanics which will be employed in this text.